Caption: Common orange lichen (Xanthoria parietina) on a rock. Lichens are organisms formed by the symbiotic association of a fungus and a green alga or cyanobacterium. They are able to produce nutrients through photosynthesis by the algal cells, and also absorb minerals from rainwater or acidic digestion of the substrate. Lichen are classified according to morphology. Foliose lichen, which include Xanthoria species, have branches with flattened leaf-like structures. This lichen is commonly found on trees, twigs, rocks and walls. It also known as yellow scale, maritime sunburst lichen and shore lichen.